States Report Medicaid Surge After Health-Law Rollout

WASHINGTON—Some states are signing up tens of thousands of new Medicaid enrollees in the initial weeks of the health law's rollout, while placing far fewer in private health insurance—a divergence that suggests Medicaid expansion may be a larger part of the law than expected.

In one sense, the Medicaid figures are good news for the Affordable Care Act's advocates, who hoped the law would reduce the number of Americans without health...